1. Field of the Invention
This invention relates to a conductive rubber elastic material, a charging member and an electrophotographic apparatus.
2. Description of the Related Art
In order that an elastic-material layer of a charging member (roller) used in a contact charging system may be provided with an electrical conductivity of approximately from 1×103 to 1×107 Ω·cm in volume resistivity, it is known that the elastic-material layer is formed by using an electronic conduction type conductive rubber composition compounded with conductive particles such as carbon black. However, such an elastic-material layer has, as stated in Japanese Patent Application Laid-open No. 2002-3651, a problem that its electrical resistance depends so strongly on the state of dispersion of the conductive particles as to tend to cause resistance non-uniformity in the roller.
In addition, electric charges present between the conductive particles change in their readiness of conduction that is due to electric-field effect, depending on applied voltage. Hence, the value of electrical resistance depends greatly on the voltage. Also, in ionic conductive materials, the mobility of ions changes depending on environmental temperature, humidity and so forth. Hence, the value of electrical resistance depends greatly on environments. Thus, both electronic conduction types and ionic conduction types have a problem in the stability of charging performance.
To cope with such a problem, proposed in Japanese Patent Application Laid-open No. 2002-3651 are, as a semiconductive rubber composition the electrical resistance value of which is settable with ease and is less dependent on voltage and less variable by environments, a semiconductive rubber composition having a matrix-domain structure containing a matrix composed of an ionically conductive rubber material and domains composed of an electronically conductive rubber material, and also a charging member making use of the same.